Demo/sockets/ftp.py

   1 # A simple FTP client.
   2 #
   3 # The information to write this program was gathered from RFC 959,
   4 # but this is not a complete implementation!  Yet it shows how a simple
   5 # FTP client can be built, and you are welcome to extend it to suit
   6 # it to your needs...
   7 #
   8 # How it works (assuming you've read the RFC):
   9 #
  10 # User commands are passed uninterpreted to the server.  However, the
  11 # user never needs to send a PORT command.  Rather, the client opens a
  12 # port right away and sends the appropriate PORT command to the server.
  13 # When a response code 150 is received, this port is used to receive
  14 # the data (which is written to stdout in this version), and when the
  15 # data is exhausted, a new port is opened and a corresponding PORT
  16 # command sent.  In order to avoid errors when reusing ports quickly
  17 # (and because there is no s.getsockname() method in Python yet) we
  18 # cycle through a number of ports in the 50000 range.
  19
  20
  21 import sys, posix, string
  22 from socket import *
  23
  24
  25 BUFSIZE = 1024
  26
  27 # Default port numbers used by the FTP protocol.
  28 #
  29 FTP_PORT = 21
  30 FTP_DATA_PORT = FTP_PORT - 1
  31
  32 # Change the data port to something not needing root permissions.
  33 #
  34 FTP_DATA_PORT = FTP_DATA_PORT + 50000
  35
  36
  37 # Main program (called at the end of this file).
  38 #
  39 def main():
  40     hostname = sys.argv[1]
  41     control(hostname)
  42
  43
  44 # Control process (user interface and user protocol interpreter).
  45 #
  46 def control(hostname):
  47     #
  48     # Create control connection
  49     #
  50     s = socket(AF_INET, SOCK_STREAM)
  51     s.connect((hostname, FTP_PORT))
  52     f = s.makefile('r') # Reading the replies is easier from a file...
  53     #
  54     # Control loop
  55     #
  56     r = None
  57     while 1:
  58         code = getreply(f)
  59         if code in ('221', 'EOF'): break
  60         if code == '150':
  61             getdata(r)
  62             code = getreply(f)
  63             r = None
  64         if not r:
  65             r = newdataport(s, f)
  66         cmd = getcommand()
  67         if not cmd: break
  68         s.send(cmd + '\r\n')
  69
  70
  71 # Create a new data port and send a PORT command to the server for it.
  72 # (Cycle through a number of ports to avoid problems with reusing
  73 # a port within a short time.)
  74 #
  75 nextport = 0
  76 #
  77 def newdataport(s, f):
  78     global nextport
  79     port = nextport + FTP_DATA_PORT
  80     nextport = (nextport+1) % 16
  81     r = socket(AF_INET, SOCK_STREAM)
  82     r.bind((gethostbyname(gethostname()), port))
  83     r.listen(1)
  84     sendportcmd(s, f, port)
  85     return r
  86
  87
  88 # Send an appropriate port command.
  89 #
  90 def sendportcmd(s, f, port):
  91     hostname = gethostname()
  92     hostaddr = gethostbyname(hostname)
  93     hbytes = string.splitfields(hostaddr, '.')
  94     pbytes = [repr(port//256), repr(port%256)]
  95     bytes = hbytes + pbytes
  96     cmd = 'PORT ' + string.joinfields(bytes, ',')
  97     s.send(cmd + '\r\n')
  98     code = getreply(f)
  99
 100
 101 # Process an ftp reply and return the 3-digit reply code (as a string).
 102 # The reply should be a line of text starting with a 3-digit number.
 103 # If the 4th char is '-', it is a multi-line reply and is
 104 # terminate by a line starting with the same 3-digit number.
 105 # Any text while receiving the reply is echoed to the file.
 106 #
 107 def getreply(f):
 108     line = f.readline()
 109     if not line: return 'EOF'
 110     print line,
 111     code = line[:3]
 112     if line[3:4] == '-':
 113         while 1:
 114             line = f.readline()
 115             if not line: break # Really an error
 116             print line,
 117             if line[:3] == code and line[3:4] != '-': break
 118     return code
 119
 120
 121 # Get the data from the data connection.
 122 #
 123 def getdata(r):
 124     print '(accepting data connection)'
 125     conn, host = r.accept()
 126     print '(data connection accepted)'
 127     while 1:
 128         data = conn.recv(BUFSIZE)
 129         if not data: break
 130         sys.stdout.write(data)
 131     print '(end of data connection)'
 132
 133 # Get a command from the user.
 134 #
 135 def getcommand():
 136     try:
 137         while 1:
 138             line = raw_input('ftp.py> ')
 139             if line: return line
 140     except EOFError:
 141         return ''
 142
 143
 144 # Call the main program.
 145 #
 146 main()